The situation is as follows:

Thread A                                               Thread B
fd = socket(AF_NETLINK, NETLINK_GENERIC);
ret = bind(fd)
select(fd)
                                                       close(fd) 

After close(fd), thread A would not be woken up.

Are you sure? netlink_release() is supposed to be called when the last reference of socket fd is gone, since Thread A is still select()'ing, how could it be released?

Also, you misunderstand release_sock(), it is paired with lock_sock(). sock_release() is called when the last fd reference is gone and it is independent to socket type:

static int sock_close(struct inode *inode, struct file *filp)
{
        sock_release(SOCKET_I(inode));
        return 0;
}